// -*- mode:c++; tab-width:2; indent-tabs-mode:nil; c-basic-offset:2 -*-

/*
 * Copyright (C) 2010-2011 ZXing authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <zxing/common/StringUtils.h>
#include <zxing/DecodeHints.h>

using namespace std;
using namespace zxing;
using namespace zxing::common;

// N.B.: these are the iconv strings for at least some versions of iconv

char const *const StringUtils::PLATFORM_DEFAULT_ENCODING = "UTF-8";
char const *const StringUtils::ASCII = "ASCII";
char const *const StringUtils::SHIFT_JIS = "SHIFT_JIS";
char const *const StringUtils::GB2312 = "GBK";
char const *const StringUtils::EUC_JP = "EUC-JP";
char const *const StringUtils::UTF8 = "UTF-8";
char const *const StringUtils::ISO88591 = "ISO8859-1";
const bool StringUtils::ASSUME_SHIFT_JIS = false;

string
StringUtils::guessEncoding(char *bytes, int length,
                           Hashtable const &hints) {
    Hashtable::const_iterator i = hints.find(DecodeHints::CHARACTER_SET);
    if (i != hints.end()) {
        return i->second;
    }
    typedef bool boolean;
    // For now, merely tries to distinguish ISO-8859-1, UTF-8 and Shift_JIS,
    // which should be by far the most common encodings.
    boolean canBeISO88591 = true;
    boolean canBeShiftJIS = true;
    boolean canBeUTF8 = true;
    int utf8BytesLeft = 0;
    //int utf8LowChars = 0;
    int utf2BytesChars = 0;
    int utf3BytesChars = 0;
    int utf4BytesChars = 0;
    int sjisBytesLeft = 0;
    //int sjisLowChars = 0;
    int sjisKatakanaChars = 0;
    //int sjisDoubleBytesChars = 0;
    int sjisCurKatakanaWordLength = 0;
    int sjisCurDoubleBytesWordLength = 0;
    int sjisMaxKatakanaWordLength = 0;
    int sjisMaxDoubleBytesWordLength = 0;
    //int isoLowChars = 0;
    //int isoHighChars = 0;
    int isoHighOther = 0;

    typedef char byte;
    boolean utf8bom = length > 3 &&
                      bytes[0] == (byte) 0xEF &&
                      bytes[1] == (byte) 0xBB &&
                      bytes[2] == (byte) 0xBF;

    for (int i = 0;
         i < length && (canBeISO88591 || canBeShiftJIS || canBeUTF8);
         i++) {

        int value = bytes[i] & 0xFF;

        // UTF-8 stuff
        if (canBeUTF8) {
            if (utf8BytesLeft > 0) {
                if ((value & 0x80) == 0) {
                    canBeUTF8 = false;
                } else {
                    utf8BytesLeft--;
                }
            } else if ((value & 0x80) != 0) {
                if ((value & 0x40) == 0) {
                    canBeUTF8 = false;
                } else {
                    utf8BytesLeft++;
                    if ((value & 0x20) == 0) {
                        utf2BytesChars++;
                    } else {
                        utf8BytesLeft++;
                        if ((value & 0x10) == 0) {
                            utf3BytesChars++;
                        } else {
                            utf8BytesLeft++;
                            if ((value & 0x08) == 0) {
                                utf4BytesChars++;
                            } else {
                                canBeUTF8 = false;
                            }
                        }
                    }
                }
            } //else {
            //utf8LowChars++;
            //}
        }

        // ISO-8859-1 stuff
        if (canBeISO88591) {
            if (value > 0x7F && value < 0xA0) {
                canBeISO88591 = false;
            } else if (value > 0x9F) {
                if (value < 0xC0 || value == 0xD7 || value == 0xF7) {
                    isoHighOther++;
                } //else {
                //isoHighChars++;
                //}
            } //else {
            //isoLowChars++;
            //}
        }

        // Shift_JIS stuff
        if (canBeShiftJIS) {
            if (sjisBytesLeft > 0) {
                if (value < 0x40 || value == 0x7F || value > 0xFC) {
                    canBeShiftJIS = false;
                } else {
                    sjisBytesLeft--;
                }
            } else if (value == 0x80 || value == 0xA0 || value > 0xEF) {
                canBeShiftJIS = false;
            } else if (value > 0xA0 && value < 0xE0) {
                sjisKatakanaChars++;
                sjisCurDoubleBytesWordLength = 0;
                sjisCurKatakanaWordLength++;
                if (sjisCurKatakanaWordLength > sjisMaxKatakanaWordLength) {
                    sjisMaxKatakanaWordLength = sjisCurKatakanaWordLength;
                }
            } else if (value > 0x7F) {
                sjisBytesLeft++;
                //sjisDoubleBytesChars++;
                sjisCurKatakanaWordLength = 0;
                sjisCurDoubleBytesWordLength++;
                if (sjisCurDoubleBytesWordLength > sjisMaxDoubleBytesWordLength) {
                    sjisMaxDoubleBytesWordLength = sjisCurDoubleBytesWordLength;
                }
            } else {
                //sjisLowChars++;
                sjisCurKatakanaWordLength = 0;
                sjisCurDoubleBytesWordLength = 0;
            }
        }
    }

    if (canBeUTF8 && utf8BytesLeft > 0) {
        canBeUTF8 = false;
    }
    if (canBeShiftJIS && sjisBytesLeft > 0) {
        canBeShiftJIS = false;
    }

    // Easy -- if there is BOM or at least 1 valid not-single byte character (and no evidence it can't be UTF-8), done
    if (canBeUTF8 && (utf8bom || utf2BytesChars + utf3BytesChars + utf4BytesChars > 0)) {
        return UTF8;
    }
    // Easy -- if assuming Shift_JIS or at least 3 valid consecutive not-ascii characters (and no evidence it can't be), done
    if (canBeShiftJIS &&
        (ASSUME_SHIFT_JIS || sjisMaxKatakanaWordLength >= 3 || sjisMaxDoubleBytesWordLength >= 3)) {
        return SHIFT_JIS;
    }
    // Distinguishing Shift_JIS and ISO-8859-1 can be a little tough for short words. The crude heuristic is:
    // - If we saw
    //   - only two consecutive katakana chars in the whole text, or
    //   - at least 10% of bytes that could be "upper" not-alphanumeric Latin1,
    // - then we conclude Shift_JIS, else ISO-8859-1
    if (canBeISO88591 && canBeShiftJIS) {
        return (sjisMaxKatakanaWordLength == 2 && sjisKatakanaChars == 2) ||
               isoHighOther * 10 >= length
               ? SHIFT_JIS : ISO88591;
    }

    // Otherwise, try in order ISO-8859-1, Shift JIS, UTF-8 and fall back to default platform encoding
    if (canBeISO88591) {
        return ISO88591;
    }
    if (canBeShiftJIS) {
        return SHIFT_JIS;
    }
    if (canBeUTF8) {
        return UTF8;
    }
    // Otherwise, we take a wild guess with platform encoding
    return PLATFORM_DEFAULT_ENCODING;
}
